Morphophysiological Characterisation of Guayule (Parthenium argentatum A. Gray) in Response to Increasing NaCl Concentrations: Phytomanagement and Phytodesalinisation in Arid and Semiarid Areas.

Water and soil salinity continuously rises due to climate change and irrigation with reused waters. Guayule (Parthenium argentatum A. Gray) is a desert perennial shrub native to northern Mexico and the southwestern United States; it is known worldwide for rubber production and is suitable for cultivation in arid and semiarid regions, such as the Mediterranean. In the present study, we investigated the effects of high and increasing concentrations of sodium chloride (NaCl) on the growth and the morphophysiological and biochemical characteristics of guayule to evaluate its tolerance to salt stress and suitability in phytomanagement and, eventually, the phytodesalinisation of salt-affected areas. Guayule originates from desert areas, but has not been found in salt-affected soils; thus, here, we tested the potential tolerance to salinity of this species, identifying the toxicity threshold and its possible sodium (Na) accumulation capacity. In a hydroponic floating root system, guayule seedlings were subjected to salinity-tolerance tests using increasing NaCl concentrations (from 2.5 to 40 g L-1 and from 43 to 684 mM). The first impairments in leaf morphophysiological traits appeared after adding 15 g L-1 (257 mM) NaCl, but the plants survived up to the hypersaline conditions of 35-40 g L-1 NaCl (about 600 mM). The distribution of major cell cations modulated the high Na content in the leaves, stems and roots; Na bioconcentration and translocation factors were close to one and greater than one, respectively. This is the first study on the morphophysiological and (bio)chemical response of guayule to different high and increasing levels of NaCl, showing the parameters and indices useful for identifying its salt tolerance threshold, adaptative mechanisms and reclamation potential in high-saline environments.

Production of bioactive and aroma volatile compounds of Lawsonia inermis L. cultivated under different growth conditions.

The present study aimed to investigate the influence of different growing conditions on the amount of leaf pigments (chlorophylls, carotenoids), bioactive metabolites, such as polyphenols, flavonoids, lawsone and volatile organic compounds (VOCs) of Lawsonia inermis L. (henna) plants. Young henna plants were cultivated for two months in a growth chamber (GC) and in open-air conditions during summer under the Mediterranean climate (OF), and leaves were analysed to evaluate their adaptive responses. The different growth conditions modified the carbon allocation priorities, increasing antioxidant metabolites (e.g. phenolic and flavonoid compounds) while decreasing lawsone in GC conditions. Quali-quantitative changes were observed for VOCs. This study revealed that GC conditions permit an alternative use of Lawsonia cultivation, because of the increase in the endogenous content of bioactive secondary metabolites with many potential biological activities.

Response to Hypersalinity of Four Halophytes Growing in Hydroponic Floating Systems: Prospects in the Phytomanagement of High Saline Wastewaters and Extreme Environments.

Hypersaline environments occur naturally worldwide in arid and semiarid regions or in artificial areas where the discharge of highly saline wastewaters, such as produced water (PW) from oil and gas industrial setups, has concentrated salt (NaCl). Halophytes can tolerate high NaCl concentrations by adopting ion extrusion and inclusion mechanisms at cell, tissue, and organ levels; however, there is still much that is not clear in the response of these plants to salinity and completely unknown issues in hypersaline conditions. Mechanisms of tolerance to saline and hypersaline conditions of four different halophytes (Suaeda fruticosa (L.) Forssk, Halocnemum strobilaceum (Pall.) M. Bieb., Juncus maritimus Lam. and Phragmites australis (Cav.) Trin. ex Steudel) were assessed by analysing growth, chlorophyll fluorescence and photosynthetic pigment parameters, nutrients, and sodium (Na) uptake and distribution in different organs. Plants were exposed to high saline (257 mM or 15 g L-1 NaCl) and extremely high or hypersaline (514, 856, and 1712 mM or 30, 50, and 100 g L-1 NaCl) salt concentrations in a hydroponic floating culture system for 28 days. The two dicotyledonous S. fruticosa and H. strobilaceum resulted in greater tolerance to hypersaline concentrations than the two monocotyledonous species J. maritimus and P. australis. Plant biomass and major cation (K, Ca, and Mg) distributions among above- and below-ground organs evidenced the osmoprotectant roles of K in the leaves of S. fruticosa, and of Ca and Mg in the leaves and stem of H. strobilaceum. In J. maritimus and P. australis the rhizome modulated the reduced uptake and translocation of nutrients and Na to shoot with increasing salinity levels. S. fruticosa and H. strobilaceum absorbed and accumulated elevated Na amounts in the aerial parts at all the NaCl doses tested, with high bioaccumulation (from 0.5 to 8.3) and translocation (1.7-16.2) factors. In the two monocotyledons, Na increased in the root and rhizome with the increasing concentration of external NaCl, dramatically reducing the growth in J. maritimus at both 50 and 100 g L-1 NaCl and compromising the survival of P. australis at 30 g L-1 NaCl and over after two weeks of treatment.

Functional responses of two Mediterranean pine species in an ozone Free-Air Controlled Exposure (FACE) experiment.

Effects of the phytotoxic and widespread ozone (O3) pollution may be species specific, but knowledge on Mediterranean conifer responses to long-term realistic exposure is still limited. We examined responses regarding to photosynthesis, needle biochemical stress markers and carbon and nitrogen (N) isotopes of two Mediterranean pine species (Pinus halepensis Mill. and Pinus pinea L.). Seedlings were grown in a Free-Air Controlled Exposure experiment with three levels of O3 (ambient air, AA [38.7 p.p.b. as daily average]; 1.5 × AA and 2.0 × AA) during the growing season (May-October 2019). In P. halepensis, O3 caused a significant decrease in the photosynthetic rate, which was mainly due to a reduction of both stomatal and mesophyll diffusion conductance to CO2. Isotopic analyses indicated a cumulative or memory effect of O3 exposure on this species, as the negative effects were highlighted only in the late growing season in association with a reduced biochemical defense capacity. On the other hand, there was no clear effect of O3 on photosynthesis in P. pinea. However, this species showed enhanced N allocation to leaves to compensate for reduced photosynthetic N- use efficiency. We conclude that functional responses to O3 are different between the two species determining that P. halepensis with thin needles was relatively sensitive to O3, while P. pinea with thicker needles was more resistant due to a potentially low O3 load per unit mass of mesophyll cells, which may affect species-specific resilience in O3-polluted Mediterranean pine forests.

Upside down and the game of C allocation.

Non-structural carbohydrates (NSCs) represent the primary carbon (C) reserves and play a crucial role for plant functioning and resilience. Indeed, these compounds are involved in the regulation between C supply and demand, and in the maintenance of hydraulic efficiency. NSCs are stored in parenchyma of woody organs, which is recognized as a proxy for reserve storage capacity of tree. Notwithstanding the importance of NSCs for tree physiology, their long-term regulation and trade-offs against growth were not deeply investigated. This work evaluated the long-term dynamics of mature tree reserves in stem and root, proxied by parenchyma features, and focusing on the trade off and interplay between the resources allocation in radial growth and reserves in stem and coarse root. In a Mediterranean beech forest, NSCs content, stem and root wood anatomy analysis, and eddy covariance data, were combined. The parenchyma fraction (RAP) of beech root and stem was different, due to differences in axial parenchyma (AP) and narrow ray parenchyma (nRP) fractions. However, these parenchyma components and radial growth showed synchronous inter-annual dynamics between the two organs. In beech stem, positive correlations were found among soluble sugars content and nRP, and among starch content and the AP. Positive correlations were found among Net Ecosystem Exchange (NEE) and AP of both organs. In contrast, NEE was negatively correlated to radial growth of root and stem. Our results suggest a different contribution of stem and roots to reserves storage, and a putative partitioning in the functional roles of parenchyma components. Moreover, a long-term trade-off of C allocation between growth and reserve pool was evidenced. Indeed, in case of C source reduction, trees preferentially allocate C towards reserves pool. Conversely, in high productive years, growth represents the major C sink.

Above- and belowground interplay: Canopy CO2 uptake, carbon and nitrogen allocation and isotope fractionation along the plant-ectomycorrhiza continuum.

In forests, mycorrhizal fungi regulate carbon (C) and nitrogen (N) dynamics. We evaluated the interplay among ectomycorrhizas (ECM), ecosystem C fluxes, tree productivity, C and N exchange and isotopic fractionation along the soil-ECM-plant continuum in a Mediterranean beech forest. From bud break to leaf shedding, we monitored: net ecosystem exchange (NEE, a measure of the net exchange of C between an ecosystem and the atmosphere), leaf area index, stem growth, N concentration, δ13 C and δ15 N in rhizosphere soil, ectomycorrhizal fine root tips (ERT), ECM-free fine root portions (NCR) and leaves. Seasonal changes in ERT relative biomass were strictly related to NEE and mimicked those detected in the radial growth. The analysis of δ13 C in ERT, leaves and NCR highlighted the impact of canopy photosynthesis on ERT development and an asynchronous seasonal C allocation strategy between ERT and NCR at the root tips level. Concerning N, δ15 N of leaves was negatively related to that of ERT and dependent on seasonal 15 N differences between ERT and NCR. Our results unravel a synchronous C allocation towards ERT and tree stem driven by the increasing NEE in spring-early summer. Moreover, they highlighted a phenology-dependent 15 N fractionation during N transfer from ECM to their hosts. This evidence, obtained in mature beech trees under natural conditions, may improve the knowledge of Mediterranean forests functionality.

Consequences of Grazing Cessation for Soil Environment and Vegetation in a Subalpine Grassland Ecosystem.

Areas covered by seminatural grasslands have been in constant decline for decades in Europe. This trend is particularly strong for mountain territories, where such traditional agricultural practices as cattle grazing are no longer economically feasible. This study was conducted in the subalpine pasture of Cinte Tesino (TN, Italy), where local farmers have applied the following different management strategies: shorter and longer grazing durations during the season and a complete abandonment for the last 15 years. We aimed to study how these different management strategies impact the functioning and diversity of vegetation and the chemical and biological characteristics of the soil. Species richness was higher in plots subjected to longer grazing with a prevalence of D. caespitosa in terms of biomass share. A decline in species richness in abandoned plots was accompanied by an increase in the share of other graminoids in collected biomass. A concomitant increase in leaf N concentration and light availability in grazed plots resulted in higher photosynthetic efficiency in some species, as revealed by the δ13C of plant tissues. Soils under grazing were characterised by a higher concentration of total and extractable N, almost doubled microbial biomass C and increased extracellular enzymes activity, evidencing nutrient cycling mobilization. While the microbial pool was characterised by lower mineralization rates, C was lost from the soil with 15 years of abandonment. The longer grazing season demonstrated to be the most beneficial, promoting species richness, C accumulation and better soil microbial functioning. A change in soil pH from strongly acidic to moderately acidic with longer grazing is likely one of the important factors adding to the success in the functioning of primary producers and decomposers in this site.

Short daily ultraviolet exposure enhances intrinsic water-use efficiency and delays senescence in Micro-Tom tomato plants.

Ultraviolet (UV) radiation, unless present at high doses, is recognised as a regulator of plant growth and some specific processes. The present study investigated the influence of short daily UV irradiation (15min/day, 11days) on leaf gas exchange and some biochemical and molecular markers of leaf senescence (such as stomata movements, chlorophyll breakdown, anthocyanin production, senescence-associated genes) in Micro-Tom tomato plants. The UV-induced reduction of g s (stomatal conductance) during the treatment was associated with the modified expression of some genes involved in the control of stomatal movements. We hypothesise a two-step regulation of stomatal closure involving salicylic and abscisic acid hormones. The temporal changes of g s and A net (net photosynthetic CO2 assimilation rate) along with the pigment behaviour, suggest a possible delay of leaf senescence in treated plants, confirmed by the expression levels of genes related to senescence such as SAG113 and DFR . The UV potential to induce a persistent partial inhibition of g s without severely affecting A net led to an increased iWUE (intrinsic water-use efficiency) during the 11-day treatment, suggesting a priming effect of short daily UV radiation towards drought conditions potentially useful in reducing the excess water use in agriculture.

Effects of simulated nitrogen deposition on the nutritional and physiological status of beech forests at two climatic contrasting sites in Italy.

Anthropogenic activities have resulted in a significant increase of reactive nitrogen (N) compounds in the atmosphere and a rise in N deposition on forest ecosystems. Increasing N loads impact forest productivity and health, altering tree physiological status and nutrient balance with possible beneficial and detrimental consequences. The impact of N deposition has received considerable attention by scientific research, covering medium and high latitudes, while experimental studies in the Mediterranean area are almost absent. The present study used a manipulative approach, through replicated N additions (background deposition, 30, 60 kg N ha-1yr-1) to simulate the cumulative effects of N deposition in two beech (Fagus sylvaticaL.) forests located in contrasting climatic regions of Italy. Leaf nutrients and photosynthetic pigments were tested as monitoring indicators after four years of N fertilization. Foliar N and pigment concentrations indicated not limiting N conditions at both forest sites, although changes in chlorophylls and carotenoids showed an early response of the canopy to N additions. N-to-phosphorus (P) and sulfur (S) ratios increased under elevated N fertilization, which could be partly related to the relative enhancement of foliar N concentration, and partly associated with the reduction of foliar P and S. The two eutrophic beech forests monitored were not severely affected by chronic N addition, not showing critical nutritional and physiological impairments over the short to medium period. However, the modifications in leaf nutrient and pigment compositions showed an incipient stress response and accentuated the differences induced by climatic and soil characteristics at the two sites. The potential use of nutrients and photosynthetic pigments in monitoring forest N deposition under contrasting climatic conditions and the eventual limits of manipulative experiments are discussed.

Photosynthesizing while hyperaccumulating nickel: Insights from the genus Odontarrhena (Brassicaceae).

Nickel-induced changes in photosynthetic activity were investigated in three Ni-hyperaccumulating Odontarrhena species with increasing Ni tolerance and accumulation capacity, O. muralis, O. moravensis, and O. chalcidica. Plantlets were grown in hydroponics at increasing NiSO4 concentrations (0, 0.25, and 1 mM) for one week, and the effects of Ni on growth, metal accumulation, photosynthesis, and nitrogen (N) allocation to components of the photosynthetic apparatus were analysed. Nickel treatments in O. chalcidica, and O. moravensis to a lesser extent, increased not only the photochemical efficiency of photosystem II (PSII) and the CO2 assimilation rate, but also CO2 diffusion from the atmosphere to the carboxylation sites. These two species displayed a specific increase and/or rearrangement of the photosynthetic pigments and a higher leaf N allocation to the photosynthetic components in the presence of the metal. Odontarrhena muralis displayed a decrease in photosynthetic performance at the lowest Ni concentration due to a combination of both stomatal and non-stomatal limitations. Our data represent the first complete investigation of the effects of Ni on the photosynthetic machinery in Ni hyperaccumulating plants. Our findings clearly indicate a stimulatory, hormetic-like, effect of the metal on both biophysics and biochemistry of photosynthesis in the species with the highest hyperaccumulation capacity.

Urban conditions affect soil characteristics and physiological performance of three evergreen woody species.

Physiological studies conducted mainly in metropolitan areas demonstrated that urban environments generate stressful conditions for plants. However, less attention has been paid to plant response to urban conditions in small cities. Here, we evaluated to what extent the health and physiological functions of some Mediterranean urban species [Quercus ilex L., Nerium oleander L. and Pittosporum tobira (Thunb.) W.T. Aiton] were impacted by urban and peri-urban conditions in Pisa (Italy), a small medieval city with narrow streets that impede efficient public transport causing oversized private transport. Experimental period spanned from late-summer to winter in concomitance with the sharp increase in air pollutants. Climate and air quality, soil physical and chemical properties, and plant physiological traits including leaf gas exchanges, chlorophyll fluorescence and leaf pigments were assessed. In soil, the organic carbon affected aggregates and water stability and the concentrations of some micro-elements decreased in winter. Air pollutants impaired leaf gas exchanges and photochemical processes at photosystem II, depending on species, season, and urban conditions. Shrubs were more susceptible than the tree species, highlighting that the latter adapted better to pollutants along an urban-peri-urban transect in Mediterranean environments. This study gives information on the physiological adaptability of some of the most frequent Mediterranean urban species to stressful conditions and demonstrated that, even in a small city, urban conditions influence the physiology and development of vegetation, affecting the plant health status and its ability to provide key ecosystem services.

Azospirillum baldaniorum Sp245 Induces Physiological Responses to Alleviate the Adverse Effects of Drought Stress in Purple Basil.

Azospirillum spp. are plant growth-promoting rhizobacteria (PGPR) that exert beneficial effects on plant growth and yield of agronomically important plant species. The aim of this study was to investigate the effects of a root treatment with Azospirillum baldaniorum Sp245 on hormones in xylem sap and physiological performance in purple basil (Ocimum basilicum L. cv. Red Rubin) plants grown under well-watered conditions and after removing water. Treatments with A. baldaniorum Sp245 included inoculation with viable cells (1·107 CFU mL-1) and addition of two doses of filtered culture supernatants (non-diluted 1·108 CFU mL-1, and diluted 1:1). Photosynthetic activity, endogenous level of hormones in xylem sap (salicylic acid, jasmonic acid, and abscisic acid), leaf pigments, leaf water potential, water-use efficiency (WUE), and drought tolerance were determined. Fluorescence and gas exchange parameters, as well as leaf water potential, showed that the highest dose of filtered culture supernatant improved both photosynthetic performance and leaf water status during water removal, associated with an increase in total pigments. Moreover, gas exchange analysis and carbon isotope discrimination found this bacterial treatment to be the most effective in inducing an increase of intrinsic and instantaneous WUE during water stress. We hypothesize that the benefits of bacterial treatments based on A. baldaniorum Sp245 are strongly correlated with the synthesis of phytohormones and the induction of plant-stress tolerance in purple basil.

Unravelling resilience mechanisms in forests: role of non-structural carbohydrates in responding to extreme weather events.

Extreme weather events are increasing in frequency and intensity due to global climate change. We hypothesized that tree carbon reserves are crucial for resilience of beech, buffering the source-sink imbalance due to late frosts and summer droughts, and that different components of non-structural carbohydrates (NSCs) play specific roles in coping with stressful situations. To assess the compound effects on mature trees of two extreme weather events, first a late frost in spring 2016 and then a drought in summer 2017, we monitored the phenology, radial growth and the dynamics of starch and soluble sugars in a Mediterranean beech forest. A growth reduction of 85% was observed after the spring late frost, yet not after the drought event. We observed a strong impact of late frost on starch, which also affected its dynamic at the beginning of the subsequent vegetative season. In 2017, the increase of soluble sugars, associated with starch hydrolysis, played a crucial role in coping with the severe summer drought. Non-structural carbohydrates helped to counteract the negative effects of both events, supporting plant survival and buffering source-sink imbalances under stressful conditions. Our findings indicate a strong trade-off between growth and NSC storage in trees. Overall, our results highlight the key role of NSCs on beech trees, response to extreme weather events, confirming the resilience of this species to highly stressful events. These insights are useful for assessing how forests may respond to the potential impacts of climate change on ecosystem processes in the Mediterranean area.

Influence of zinc and manganese enrichments on growth, biosorption and photosynthetic efficiency of Chlorella sp.

Treating biosolids from industrial, urban, and agricultural plants produces high amounts of water. After organic pollutants and non-essential heavy metals have been removed, these wastewaters are still rich in trace elements such as zinc (Zn), copper, or manganese (Mn) and have high conductivity and extremely variable pH. In this study, an isolated Chlorella sp. strain was grown for 21 days in nutrient solutions enriched with known amounts of Zn or Mn to obtain concentrations three (4.0 mg L-1)- and six (1.0 mg L-1)-fold higher than the basal medium levels, respectively, and over the limits permitted in aquatic environments. The green alga exhibited high tolerance to Zn and Mn, with the maximum abatement of Zn (28-30%) and Mn (60-63.5%) after 14 and 7 days of culture, respectively. Mn stimulated the growth rate and biomass production of Chlorella, which showed the highest carbon levels just in the first week. In both treatments, the nitrogen and protein contents remarkably increased. The photosynthetic pigments increased until the 14th day, with a higher extent in the Zn-enriched solution. An increasing photochemical efficiency was observed after 7 days of treatment, when the microalgae grown in Zn- and Mn-enriched solutions showed a slightly higher maximum photochemical efficiency than control. The autotrophic and controlled growth system adopted was designed to monitor the dynamic balance of Zn and Mn contents in the solutions and in the algal biomass. This system has proved to be useful in identifying the optimal nutritional conditions of the microalgae, along with the optimal temporal patterns of both metal biosorption capacity for water remediation and element bioaccumulation in the algal biomass.

Salinity-Induced Changes of Photosynthetic Performance, Lawsone, VOCs, and Antioxidant Metabolism in Lawsonia inermis L.

The present study aimed to elucidate the salinity influence on the bioactive metabolites of Lawsonia inermis L. (henna) plants. Young henna plants were cultivated under salinity stress with two NaCl concentrations (75 mM and 150 mM) in controlled environmental conditions and the leaves were investigated to check their adaptative responses. The modulation of photosynthetic performance to salinity stress was demonstrated by gas exchange and chlorophyll fluorescence parameters. The partial stomatal closure triggered an enhanced water-use efficiency, and a proline accumulation was observed, leading to an osmotic adjustment. The increased capacity to dissipate the excess excitation energy at photosystem II as heat was associated with changes in chlorophylls, anthocyanins, and carotenoids. The higher antioxidant activity at 150 mM salt level suggested its scavenger role on reactive oxygen species (ROS) dissipation and photoprotection. The reduced CO2 uptake and the higher metabolic costs necessary to sustain the henna tolerance mechanism against high NaCl concentration negatively affected lawsone production. Leaf volatile organic compounds (VOCs) showed changes in the amount and composition of VOCs with increasing salinity level. Overall, this study revealed efficient physiological and biochemical adaptations of henna leaves to salt stress despite an altered production of important economic metabolites such as lawsone.

Maintenance of photosynthetic capacity in flooded tomato plants with reduced ethylene sensitivity.

Ethylene is considered one of the most important plant hormones orchestrating plant responses to flooding stress. However, ethylene may induce deleterious effects on plants, especially when produced at high rates in response to stress. In this paper, we explored the effect of attenuated ethylene sensitivity in the Never ripe (Nr) mutant on leaf photosynthetic capacity of flooded tomato plants. We found out that reduced ethylene perception in Nr plants was associated with a more efficient photochemical and non-photochemical radiative energy dissipation capability in response to flooding. The data correlated with the retention of chlorophyll and carotenoids content in flooded Nr leaves. Moreover, leaf area and specific leaf area were higher in Nr, indicating that ethylene would exert a negative role in leaf growth and expansion under flooded conditions. Although stomatal conductance was hampered in flooded Nr plants, carboxylation activity was not affected by flooding in the mutant, suggesting that ethylene is responsible for inducing non-stomatal limitations to photosynthetic CO2 uptake. Upregulation of several cysteine protease genes and high protease activity led to Rubisco protein loss in response to ethylene under flooding. Reduction of Rubisco content would, at least in part, account for the reduction of its carboxylation efficiency in response to ethylene in flooded plants. Therefore, besides its role as a trigger of many adaptive responses, perception of ethylene entails limitations in light and dark photosynthetic reactions by speeding up the senescence process that leads to a progressive disassembly of the photosynthetic machinery in leaves of flooded tomato plants.

Photosynthetic performance of five cool-season turfgrasses under UV-B exposure.

Turfgrasses are monocotyledonous plants from the family Poaceae. They are widely used in green spaces and are considered one of the most economically important horticultural crops in the world. Turfgrass quality is affected by several environmental factors including light, which is involved in the quality decline of transplanted sod. Ultraviolet-B (UV-B) is an important regulator of plant growth and development. Plants growing and/or stored in protected systems, such as in sod production, may be more vulnerable to UV-B damage than those growing in the field due to acclimation. Few studies on the effects of UV-B on turfgrass physiology have been published. Therefore, the aim of this study was to evaluate the influence of UV-B irradiation on the photosynthetic performance of five cool-season turfgrasses, namely Agrostis stolonifera L., Festuca arundinacea Schreb., Poa supina Schrad., Poa pratensis L. and Lolium perenne L. Turfgrasses were exposed to 18.25 kJ m-2 d-1 biologically effective UV-B in growth chambers under controlled conditions. Measurements included photosynthetic pigments, chlorophyll fluorescence and gas exchanges monitored for 16 d-UV-B treatment and after recovery. Content of pigments decreased with UV-B exposure with significant differences among the species. UV-B also affected the photosystem II (PSII) efficiency depending on the exposure period and species. Similarly, gas exchange parameters showed different effects among species after UV-B exposure compromising the assimilation of CO2. Multivariate analysis highlighted three main clusters of species confirming their different UV-B tolerance and ability to restore PSII photochemistry after recovery, from which Festuca arundinacea resulted to be the most tolerant.

Physiological responses of maca (Lepidium meyenii Walp.) plants to UV radiation in its high-altitude mountain ecosystem.

Ultraviolet (UV) radiation is a small fraction of the solar spectrum, which acts as a key environmental modulator of plant function affecting metabolic regulation and growth. Plant species endemic to the Andes are well adapted to the harsh features of high-altitude climate, including high UV radiation. Maca (Lepidium meyenii Walpers) is a member of Brassicaceae family native to the central Andes of Peru, which grows between 3500 and 4500 m of altitude, where only highland grasses and few hardy bushes can survive. Even though maca has been the focus of recent researches, mainly due to its nutraceutical properties, knowledge regarding its adaptation mechanisms to these particular natural environmental conditions is scarce. In this study, we manipulated solar UV radiation by using UV-transmitting (Control) or blocking (UV-block) filters under field conditions (4138 m above the sea level) in order to understand the impact of UV on morphological and physiological parameters of maca crops over a complete growing season. Compared to the UV-blocking filter, under control condition a significant increase of hypocotyl weight was observed during the vegetative phase together with a marked leaf turnover. Although parameters conferring photosynthetic performance were not altered by UV, carbohydrate allocation between above and underground organs was affected. Control condition did not influence the content of secondary metabolites such as glucosinolates and phenolic compounds in hypocotyls, while some differences were observed in the rosettes. These differences were mainly related to leaf turnover and the protection of new young leaves in control plants. Altogether, the data suggest that maca plants respond to strong UV radiation at high altitudes by a coordinated remobilization and relocation of metabolites between source and sink organs via a possible UV signaling pathway.

A Comparison of the Variable J and Carbon-Isotopic Composition of Sugars Methods to Assess Mesophyll Conductance from the Leaf to the Canopy Scale in Drought-Stressed Cherry.

Conductance of CO2 across the mesophyll (Gm) frequently constrains photosynthesis (PN) but cannot be measured directly. We examined Gm of cherry (Prunus avium L.) subjected to severe drought using the variable J method and carbon-isotopic composition (δ13C) of sugars from the centre of the leaf, the leaf petiole sap, and sap from the largest branch. Depending upon the location of the plant from which sugars are sampled, Gm may be estimated over scales ranging from a portion of the leaf to a canopy of leaves. Both the variable J and δ13C of sugars methods showed a reduction in Gm as soil water availability declined. The δ13C of sugars further from the source of their synthesis within the leaf did not correspond as closely to the diffusive and C-isotopic discrimination conditions reflected in the instantaneous measurement of gas exchange and chlorophyll-fluorescence utilised by the variable J approach. Post-photosynthetic fractionation processes and/or the release of sugars from stored carbohydrates (previously fixed under different environmental and C-isotopic discrimination conditions) may reduce the efficacy of the δ13C of sugars from leaf petiole and branch sap in estimating Gm in a short-term study. Consideration should be given to the spatial and temporal scales at which Gm is under observation in any experimental analysis.

Energy conversion processes and related gene expression in a sunflower mutant with altered salicylic acid metabolism.

Salicylic acid (SA) is involved in several responses associated with plant development and defence against biotic and abiotic stress, but its role on photosynthetic regulation is still under debate. This work investigated energy conversion processes and related gene expression in the brachytic mutant of sunflower lingering hope (linho). This mutant was characterized by a higher ratio between the free SA form and its conjugate form SA O-ß-D-glucoside (SAG) compared to wild type (WT), without significant changes in the endogenous level of abscisic acid and hydrogen peroxide. The mutant showed an inhibition of photosynthesis due to a combination of both stomatal and non-stomatal limitations, although the latter seemed to play a major role. The reduced carboxylation efficiency was associated with a down-regulation of the gene expression for both the large and small subunits of Rubisco and the Rubisco activase enzyme. Moreover, linho showed an alteration of photosystem II (PSII) functionality, with reduced PSII photochemistry, increased PSII excitation pressure and decreased thermal energy dissipation of excessive light energy. These responses were associated with a lower photosynthetic pigments concentration and a reduced expression of genes encoding for light-harvesting chlorophyll a/b binding proteins (i.e. HaLhcA), chlorophyll binding subunits of PSII proteins (i.e. HaPsbS and HaPsbX), phytoene synthase enzyme and a different expression level for genes related to PSII repair cycle, such as HaPsbA and HaPsbD. The concomitant stimulation of respiratory metabolism, suggests that linho activated a coordinate modulation of chloroplast and mitochondria activities to compensate the energy imbalance and regulate energy conversion processes.